Pedestrian Dead Reckoning (PDR) is a method of calculating a position of a user by the computation of successive positions of the user. The successive positions are calculated using the previous position, and an estimation of the direction and speed of the movement of the user. PDR can typically be performed by a portable device carried or worn by the user, such as e.g. a smartphone. The motion sensors of the portable device thus provide an estimation of the direction and speed of the movement of the user. Compared to other methods of estimating the position of the user, PDR has the advantage of having the ability to be performed in any environment, and requiring a limited amount of resources on the portable device. On the contrary, other methods such as GPS navigation are subject to the reception of external signals which are not always available, and the reception of such signals requires a large amount of resources. There, for pedestrian indoor navigation, PDR is a solution that may be used.
However, the PDR method is subject to addition of errors. Indeed, errors of estimation of the speed or orientation of the movement of the user may lead, at each iteration of calculation of a position, to an error in the difference between the current position and the previous one. The addition of successive errors may generate, after a number of successive iterations, an increased error in the position of the user.
Methods such as Fused Location Provider (FLP) alleviate this drawback. FLP consist in determining the location of the user using a combination of different techniques and methods, such as, for example, PDR, absolute position inputs (GPS, Wi-Fi, Bluetooth signals . . . ) and/or maps. For example, and absolute input such as a GPS input may be used from time to time to reset the position of the user to an absolute position in order to avoid the addition of errors on the position over a too long period, while saving resources by limiting access to GPS signals. It is also possible to use absolute position methods as soon as absolute position inputs are available, and PDR otherwise.
Co-pending, commonly owned U.S. patent application Ser. No. 14/537,503 filed Nov. 10, 2014, which is hereby incorporated herein by reference in its entirety, discloses a trajectory tracking system, which is configured to process motion signals to perform PDR, and fuse the location obtained by PDR with absolute input data such as GPS.
The orientation of signals which are sensed by motion sensors depend on the relative orientation and position of the sensor compared to the body of the user. The determination of the relative position of the portable device to the body of the user thus permits to efficiently transform the orientation of the motion sensed by the portable device into orientation of the user.
Co-pending, commonly owned U.S. patent application Ser. No. 15/105,757 filed Jun. 17, 2016, which is hereby incorporated herein by reference in its entirety, discloses a method for continuously computing a misalignment of the orientation of a user and a portable device worn by the user. This misalignment information can be used by a PDR algorithm. However, it is difficult to separate motion that are caused by a change of orientation of the portable device relative to the user, and the motion of the user himself.